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GEOTECHNICAL ENGINEERING Soil Compression, Consolidation and Settlement by
Dr. Amizatulhani Abdullah Faculty of Civil Engineering ad Earth Resources

2. Chapter description Aims Expected Outcomes References
This chapter provides further discussion and explanation related to soil consolidation and settlement.
Expected Outcomes
Apply the fundamental of consolidation to solve problems.
Analyze case given and generate effective solution.
References
Das, B.M., “Principles of Geotechnical Engineering, 5th edition”, Thomson Learning (2002).
Raj, P.P., “Soil Mechanics & Foundation Engineering”, Prentice Hall (2008).
Liu, C. & Evett, J.B., “Soils and Foundations, 7th edition”, Prentice Hall (2008).
Whitlow, R., “Basic Soil Mechanics”, Prentice Hall (2004).
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

3. Content Compression index and swell index Time rate of consolidation
Coefficient of consolidation
Normally consolidated and over consolidated clay
Primary consolidation settlement
Secondary consolidation settlement
Conclusion
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

4. Compression index and swell index1 e1 2 e2 2 1
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

5. Recompression index / swell index, Cs =2 e2 e1 1 2 1
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

6. Time rate of consolidation
The rate at which the consolidation occurs depends mainly on the permeability of the soil and the length of drainage path.
Time rate of consolidation can be calculated using the following equation:
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

7. Variation of Uz with Tv and z/Hdr (Das, 2002)
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

8. Coefficient of consolidation
The coefficient of consolidation, cv can be calculated using the following equation :
the coefficient of volume compressibility, mv can be calculated using the following equation :
Slope of the e/’ curve
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

9. Please make sure that you know how to obtain t50 and t90 values.
Coefficient of consolidation can also be determine from oedometer test.
A) Casagrande method (logarithmic time method)
B) Taylor method (square root time method)
Please make sure that you know how to obtain t50 and t90 values.
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

10. Normally & over consolidated clay
NORMALLY CONSOLIDATED
CLAY
OVER CONSOLIDATED
CLAY
A deposit that has been fully consolidated under a certain pressure in the past, larger than the present overburden pressure. The maximum effective past pressure is called the pre-consolidation pressure, c.
If the present effective overburden pressure in the deposit is the maximum pressure to which the deposit has ever been consolidated at any time in the past.
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

11. How to determine whether the clay is normally consolidated or not?
(1) Determine the present effective overburden pressure, p.
P, kN/m2
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

12. a e
P, kN/m2
(2) By using the void ratio vs log pressure plot, locate the point designated by a pressure of p and void ratio of e.
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

13. a e
P, kN/m2
(3) Project the lower right straight line portion of e-log p curve (straight line upward and to the left).
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

14. (4) The dashed line will intersect a horizontal line drawn at e = e0. b a e
P, kN/m2
(4) The dashed line will intersect a horizontal line drawn at e = e0.
(5) If point b is located to the left of point a, the soil is normally consolidated clay.
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

15. How to determine whether the clay is over consolidated or not?
Follow step 1 to step 4 (for normal consolidated clay).
If point b is located to the right of point a, the soil is over consolidated clay.
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

16. Primary consolidation settlement
Occurred due to the expulsion/extrusion of the water that occupies the void spaces.
Primary consolidation settlement is a result of a volume change in saturated cohesive soils.
Very slow and continues over a long period of time.
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

17. How to estimate primary consolidation settlement?
For normally consolidated clay
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

18. For over consolidated clay
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

19. Soil Compression, Consolidation and Settlement by Dr
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

20. Secondary consolidation settlement
Additional form of compression that occurs at constant effective stress at a very slow rate.
Observed in saturated cohesive soils.
Result of the plastic adjustment and rearrangement of soil fabrics.
Occurs after the primary consolidation settlement ended.
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

21. How to estimate secondary compression settlement?
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

22. Work example
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

23. Data : Total load, Q = 5400kN Initial void ratio, eo = 1
Data : Total load, Q = 5400kN Initial void ratio, eo = 1.38 Compression index, Cc = 0.68 Influence coefficient, I = 0.08 Calculate the primary consolidation settlement of the soil.
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

24. Solution for work example
Determine the present effective overburden pressure, ’o
Determine the stress increment under foundation, 
Substitute all the values into equation, Sp
Ans : 0.240m
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

25. Conclusion Conclusion #1
There are several important parameters that can be obtained from oedometer result which are compression index, swell index, time rate of consolidation, coefficient of consolidation.
Conclusion #2
By using those related parameters, the settlement of soil can be estimated either in term of primary or secondary settlement.
Soil Compression, Consolidation and Settlement by Dr. Amizatulhani Abdullah

26. Author Information Dr. Amizatulhani Abdullah Dr
Author Information Dr. Amizatulhani Abdullah Dr. Mohd Yuhyi Mohd Tadza Dr. Youventharan Duraisamy Dr. Muzamir Hasan Ir. Azhani Zukri